#roll-img {
    width: 850px;
    height: 500px;
    margin: 50px auto;
    overflow: hidden;
    position: relative;
}

#roll-img ul {
    position: absolute;
    left: 0;
    top: 0;
}

#roll-img ul li {
    height: 500px;
    float: left;
}

#roll-img ol {
    position: absolute;
    right: 10%;
    bottom: 10px;
    z-index: 6
}

#roll-img ol li {
    width: 10px;
    height: 20px;
    background: #fff;
    margin-left: 5px;
    float: left;
    line-height: 20px;
    border-radius: 10px;
    cursor: pointer;
    user-select: none;
}

#roll-img ol li.active {
    background: black;
    color: #fff;
}

#roll-img>a {
    text-decoration: none;
    position: absolute;
    top: 50%;
    margin-top: -10px;
    height: 40px;
    line-height: 32px;
    text-align: center;
    width: 40px;
    font-size: 40px;
    vertical-align: middle;
    color: #fff;
    background: rgba(0, 0, 0, 0.5);
    z-index: 6;
}

#goPrev {
    left: 0;
}

#goNext {
    right: 0;
}

img {
    width: 850px;
    height: 500px;
}